The present invention relates to a non-contact inspection system for detection and identification of the type of defects in transparent media, including flat glass and moulded curved glass e.g. glass of cathode ray tube (CRT) face plates, plastic sheets, lens blanks and the like. The system is intended to operate on a continuous production line at line speed, and for the identification of a wide variety of types of defects, including bubbles, scratches, chips, cracks and other optical defects. The system is a dark view inspection system for detection and identification of light diverting and transparent defects with optical properties in transparent media.
In processes for manufacture of transparent media, it is necessary to be able to inspect the transparent media for defects. Such defects may be in the form of scratches, bubbles, chips, blemishes and a wide variety of other defects. However, the mere detection of defects is insufficient in that the manufacturer of the transparent media needs to know whether the defects are insignificant e.g. minor in nature and thus acceptable to the customer, or major flaws such the transparent media would not conform to specifications established by the customer.
It is possible to use human visual inspection of transparent media and to identify those articles of transparent media that have defects. In addition, using visual inspection, it is possible to identify the location and possibly the type of defect. However, human visual inspection is not acceptable because of the time and cost involved in conducting a visual inspection, and the limitations of such a method. It would be preferable to be able to conduct the inspection on-line in the production process, at production speeds, so that defects could be rapidly identified and communicated to production personnel and/or the articles of transparent media with the defects could be readily and quickly separated from articles meeting quality specifications in an effective manner.
Methods have been developed for the inspection of sheets of glass using optical techniques that involve use of lasers. While lasers can be very effective in the detection of defects in flat or essentially flat sheets of glass, imaging optics for laser light require a small f-stop i.e. a large aperture, and consequently the depth of field is small. This limits the usefulness of laser light, especially in circumstances where the glass or article has curvature. One example of such a curved article is the face plate of a cathode ray tube (CRT), which requires good optical properties. Focusing on the surface of a curved article to detect defects is difficult if the depth of field of the imaging optics is small.
Apparatus and a method have now been found that is particularly intended for use in inspection of curved articles of transparent media in a production line, at production speeds, in a manner that shows the magnitude, type and location of the defects in the transparent media.
Accordingly, one aspect of the present invention provides an apparatus for the detection and identification of light diverting and transparent defects with optical properties in a transparent medium, comprising:
a) a light source of extended length and width;
b) a lens system to form a column of light from said light source and to focus said light at a plane;
c) an optical recording device located at said plane;
d) an aperture stop located at said source of light, said lens system focusing an image of said aperture stop at said plane, said optical recording device being located at said image; and
e) means to pass said transparent medium through said column of light.
Another aspect of the present invention provides a method for detection and identification of light diverting and transparent defects with optical properties in a transparent medium, comprising:
a) passing said transparent medium through a column of light from a source of light having an aperture stop therein;
b) focusing said column of light at a plane, an image of said aperture stop being focused at said plane, said plane having an optical recording device at said image of said aperture stop; and
c) recording light from a light diverting and transparent defect with optical properties in said transparent medium with said optical recording device.
A further aspect of the present invention provides a method for the detection and identification of light diverting and transparent defects with optical properties in a transparent medium, comprising:
a) passing light through a transparent medium;
b) providing an aperture stop in said light, and focusing said aperture stop at an optical recording device;
c) measuring intensity of light diverted by a light diverting and transparent defect with optical properties in said transparent medium using said optical recording device.
Another aspect of the present invention provides apparatus for the detection of defects in a transparent medium, comprising:
a) a viewing area inspection system for the transparent medium;
b) a dark view inspection system for the transparent medium; and
c) means to pass said transparent medium through said viewing area inspection system and said dark view inspection system, in sequence.
Yet another aspect of the present invention provides apparatus for the detection and identification of light diverting and transparent defects with optical properties in a transparent medium, comprising:
a) first and second light sources of extended length and width, each light source providing a column of light;
b) a first optical recording device associated with the first light source and a second optical recording device associated with the second light source;
c) means to pass said transparent medium through said columns of light;
d) said second light source having an aperture stop and a lens system to form a column of light from said light source and to focus said light at a plane, a lens system focusing an image of said aperture stop at said plane, said second optical recording device being located at said image.
A further aspect of the present invention provides a method for the detection and identification of defects in a transparent medium, comprising:
a) passing said transparent medium through first and second light sources of extended length and width, each light source providing a column of light;
b) focusing the column of light from the first light source at a first optical recording device and focusing the column of light from the second light source at a second optical recording device;
c) recording images of said transparent medium at said first and second optical recording devices; and
d) combining said images for detection and identification of the defects.